The present disclosure relates generally to an imaging module and an imaging reader for, and a method of, reading targets, such as bar code symbols, to be electro-optically read by image capture with a substantially constant resolution over an extended range of working distances away from the module/reader.
Solid-state imaging systems or imaging readers have long been used, in both handheld and hands-free modes of operation, in many industries, such as retail, manufacturing, warehousing, distribution, postal, transportation, logistics, etc., to electro-optically read targets, such as one- or two-dimensional bar code symbols to be decoded. A known imaging reader generally includes an imaging module, also known as a scan engine, that is mounted in a housing, and that typically has an illumination system for emitting illumination light toward the targets for reflection and scattering therefrom; and an imaging system having a solid-state imager, also known as an imaging sensor, with an array of light sensors or pixels, and an imaging lens assembly for capturing return illumination light scattered and/or reflected from the illuminated targets over a field of view, and for projecting the captured illumination light onto the imager to initiate capture of an image of each target. The imager produces electrical signals that are decoded and/or processed by a programmed microprocessor or controller into information related to each target being read, e.g., decoded data identifying each target. The controller is operative for transmitting the decoded data, either via a wireless or wired link, to a remote host for further processing, e.g., price retrieval from a price database to obtain a price for each identified target.
The known imaging lens assembly may be a fixed focus type and be comprised of a plurality or group of stationary lenses, such as a classical Cooke triplet having a center lens between a pair of side lenses. In order to image targets that can be located over an extended range of working distances relative to the reader, it is known to configure the fixed focus reader with different lens configurations having different focal lengths, each designed to focus at a different working distance. However, such multiple lens configurations are costly and not readily versatile across a broad range of applications.
The known imaging lens assembly may also be a variable focus type and be comprised of one or more movable lenses, which are moved, for example, by a voice coil motor, to automatically focus a target between a near or close-in working distance close to the reader and a remote or far-out working distance further away from the reader. However, this mechanical lens movement is disadvantageous for several reasons. First, the mechanical lens movement generates vibrations which, in the case of a handheld reader, may be propagated through the reader to the user's hand, may generate dust to obscure the lenses, and may generate an objectionable, annoying, audible hum. In addition, the voice coil motor is very susceptible to hand motion, consumes electrical power, is expensive and notoriously slow, can be unreliable, occupies space, and increases the overall weight, size and complexity of the reader.
Another problem associated with the known imaging readers relates to the resolution or detail in which the image of each target is captured. A far-out target located at the far-out working distance is best read by the imager with a high resolution over a relatively narrow field of view, because the apparent size of the far-out target is relatively small. A close-in target located at the close-in working distance is best read by the imager over a relatively wide field of view, because its apparent size is relatively large, and a high resolution for the imager is not needed due to the close proximity of the close-in target. A multi-megapixel imager could provide the high resolution for the far-out target, but such an imager is not only expensive, but dealing with such a large number of pixels slows down the frame rate of the imager and also slows down the processing of the electrical signals to be decoded and processed. Such time delays negatively impacts the aggressiveness of the reader and may render its performance as too sluggish in many applications.
Accordingly, it would be desirable to electro-optically and expeditiously read targets by image capture over an extended range of working distances at a substantially constant resolution.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The module, reader and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.